A great amount of waste portions of fish, which are generally considered useless or untapped, had been discarded. This has been one of the major problems that we should address in the modern society to find various ways to use that seemingly unserviceable portion of fishes in many applicable fields. In view of collagen being obtained from mammals and widely available as an edible material, researches are now being made about fish collagen and in particular about salmon and trout skins, in which a collagen is a main ingredient of the tissues. Recent years, thus, have seen some methods proposed to extract and produce a collagen from fish skins, including the skins of salmon and trout in question. The fish skin collagen, however, differs in characteristics from mammalian collagen and requires relatively less harse treatment due to the more delicate matrix of the skin. Collagen products have a number of applications in various industries. In one such application, collagen powders are used in clarification or precipitation processes, for example for clarifying potable liquors such as beer and wine. During the fermentation of liquors various particulate materials such as yeasts and proteins become suspended in the liquor and need to be removed. Collagen findings are added to the liquor to clarify it by aiding the precipitation of the suspended materials. Collagen and gelatin can also be used in juice clarification processes.
Collagen is generally prepared from fish isinglass, which constitutes a very pure source of collagen prepared from the dried swim bladders of fish. Many investigations have been made into the extraction of collagen from animal and fish skins including cold water fish skins (U.S. Pat. Nos. 4,295,894, 5,698,228, 5,162,506, 5,420,248, JP 4037679, JP 9278639, JP 2-291814, PL 312122, RU 2139937). The collagen extraction processes known involve a wide range of chemical and mechanical extractions, or combinations thereof. The properties of the collagen products obtained by these processes vary widely. Many of the extraction processes applied to fish skins are adaptations and modifications of mammalian collagen extraction techniques. The applicants have identified that many of the processing steps applied to mammalian collagen extraction are not directly applicable for fish skin collagen extraction since the treatment may be quite harsh or too strong for the fish skin matrix. Such steps include chemical washes and extractions with strong acids or alkali, excessive filtering and decantation steps amongst others. A simplified extraction process which eliminates many of these steps would be desirable to increase yield and to reduce denaturation of the extracted collagen.
Collagen is recognized as a difficult and expensive protein to quantify because of the insoluble nature of most collagens. Yet, solubility is a key functional property important in a variety of applications such as healthcare products. The applicants have also determined that the conformation of the native collagen molecule determines molecular functionality, with transition to the random coiled confirmation of gelatin upon denaturing resulting in a significant loss in fining ability. Collagen has also been reported to be extracted from several fish species such as hake (Merluccius merluccius L.), yellow sea-bream (Dentex tumiforms), tiger puffer (Takifugu rubripes), carp (Cyprimus carpio); squids (Illex argentinus) (Ilona Kolodziejska, 1999); and also jellyfish (Rhopilema asamushi) (Takeshi Nagai et. al, 2000). All procedures reported were very similar where non-enzymatic extractions were employed and, if enzymatic reactions were used, then pepsin was the most common enzyme.
The use of by-products from fish processing for collagen and gelatine production, as an alternative introduces some questions, the diversity of aquatic species and also the higher susceptibility of this collagen to deterioration when compared to those from mammals, which is more stable and facilitates its preservation (Fernandez-Diaz et al., 2003). Moreover, after degutting and filleting of fish, skins are kept with the rest of the discard and they are subjected to rapid enzymatic and microbial damage, which are natural and this may lead to quality variation of the extracted collagen and the gelatins. Enzymatic activities in aquatic animals are known to be higher than land animals.
Collagen exists in several polymorphic forms, the common ones are Type I, III and V; type II and IV which are uncommon and can only be found in certain collagens, which have also been reported (Foegeding et al., 2001). Collagens and their denatured forms, gelatines, are composed of long chains of amino acids, connected by peptide bonds (Ockerman and Hansen, 1988; Ward and Courts, 1977). The number and type of chemical covalent bonds between the chains are altered as the animal ages, fewer numbers in younger animals. This influences the molecular properties of the resultant gelatine and glue (Ockerman and Hansen, 1988). Fish collagens, in general, have lower amino acids contents than mammalian collagens and this may be the reason for the lower denaturation temperature (Grossman and Bergman, 1992, Jamilah and Harvinder, 2002). This in turn appears to be related to the body temperature of the species (Johns, 1977). There are many properties of collagen that make it an attractive substance for various medical applications, such as for implants, transplants, organ replacement, tissue equivalents, vitreous replacements, plastic and cosmetic surgery, surgical suture, surgical dressings for wounds, burns, etc. (See e.g., U.S. Pat. Nos. 5,106,949, 5,104,660, 5,081,106, 5,383,930, 4,485,095, 4,485,097, 4,539,716, 4,546,500, 4,409,332, 4,604,346, 4,835,102, 4,837,379, 3,800,792, 3,491,760, 3,113,568, 3,471,598, 2,202,566, and 3,157,524, all of which are incorporated herein by reference; Prudden, Arch. Surg. 89:1046-1059 [1964]; and Peacock et al. Ann. Surg., 161:238-247 [1965]). For example, by itself, collagen is a relatively weak immunogen, at least partially due to the masking of potential antigenic determinants within the collagen structure. Also, it is resistant to proteolysis due to its helical structure. In addition, it is a natural substance for cell adhesion and the major tensile load-bearing component of the musculoskeletal system. Thus, extensive efforts have been devoted to the production of collagen fibers and membranes suitable for use in medical, as well as veterinary applications. Collagens have been actively incorporated in beverage formulations (both instant and traditional), of late.